How works memory? - podcast – Fondation Ipsen

The human brain is extraordinary! we can save about a million billion bits, far more than any computer. We keep information constantly, at the same speed we forget others.

What is memory?

Memory is the function that allows us to record, store and retrieve information to interact with our environment, perform everyday tasks, and so on. It brings together know-how, knowledge, memories, sensory information, etc. It is indispensable for the reflection and the projection of everyone in the future.

However, there are several categories of memory.

Short-term memory or working memory. It is the memory of the present and we constantly use it. As the name suggests, it retains information for a few seconds. On the other hand, memories are quickly forgotten and are therefore necessarily linked to long-term memory. It’s a bit like the RAM of a computer.
To memorize information, we can use different strategies: a phonological loop (we repeat the information several times) or a visuospatial notebook (we will imagine the information: color, size, appearance, etc.).

Long-term memory is broken down into different memory systems: explicit or declarative memory and implicit memory. The explicit memory concerns the memorization of information that we can express with words, it is the semantic memory, and the one that relates to time, the episodic memory.

Semantic memory, which is the memory of knowledge. It records data, either personal or from our environment. These data are accessible to our consciousness and can easily be brought out.

Episodic memory allows one to remember past moments (autobiographical events) and to predict the next day. It allows us to situate ourselves in time and space and, thus, to project ourselves into the future.
In addition, all, or parts of, these memories disappear with time. The memories are transformed into general knowledge. In this case, forgetting is perfectly normal, even if it favors amalgam.

Procedural memory. This is the memory of automatisms (cycling, walking, driving, etc.). It is a functioning memory that restores information without conscious control and where neural circuits are automated.

And finally, the perceptive memory, Perceptual memory is dependent on one’s sensory faculties and works without our knowledge. We will memorize, without realizing, a wide variety of information (images, sounds, smells, etc.). This memory allows us to remember faces, places, voices, smells, flavors, etc.

How does memory work?

Our memory works much differently than a computer. Indeed, just for the memory, several areas are involved in the storage of information. During this process, the hippocampus has a central role. This brain area, shaped like a horseshoe, is located in a very old part of our brain. It is essential for short-term memory and episodic memory. A destruction of this structure does not allow the acquisition of new information but does not prevent the restitution of old memories recorded in the long-term memory. The hippocampus is a crossroads that connects to different areas of the brain to record the different types of information to be retained (frontal cortex, temporal cortex, cerebellum, etc.).

All memory systems use separate but interconnected neural networks. Neural networks are very numerous in the brain. Indeed, a neuron will connect with 10,000 other cells and will receive information from 100,000 neuronal extensions. The contact between two neurons, between the extension of the emitting neuron and the body of the receiving neuron, is called a synapse. However, the storage results from a modification of the connections between the neurons of a memory system. We speak of “synaptic plasticity”. Thus, to create a memory, chemical signals will be produced to form new synapses. Therefore, for each memory, there is a specific and unique network of interconnected neurons. Regular and repeated activation reinforces these connections, with the consequence of consolidating the memory or, on the contrary, of forgetting it. Thus, forgetting is an important part of the proper functioning of memory. This function makes it possible to establish new connections.

However, when do forgetfulness become abnormally numerous and abnormal to suspect a pathology, or even a dementia such as Alzheimer’s disease?

Brain dementia

According to the WHO, brain dementia is an evolving and chronic syndrome in which cognitive function deteriorates, namely: deterioration of memory, reasoning, behavior, orientation, language, learning or of the ability to perform daily tasks. This kind of disease is therefore much more important than normal aging. Indeed, with age, the brain gradually loses its ability to form new connections, but do not seriously interfere with brain function.
Thus, the omissions of everyday life have nothing in common with those found of people with dementia. Forgetting where we left our keys can be common and is especially a sign of lack of attention. But, forgetting to pick up your grandchildren at school several times in a row is a worrying sign.

Dementia is one of the leading causes of disability and dependency among the elderly in the world. It is very stressful for the patients, but also for their entourage, the caregivers. There are 50 million people worldwide that are affected by it, and there are about 10 million new cases each year (an estimated 152 million by 2050).

Alzheimer’s disease, ischemic dementia (which occurs after a stroke), fronto-temporal dementia, Levi’s body dementia and some other types (Creutzfeld Jakob, etc.) are part of brain dementia. All these diseases are associated with a loss of neurons, and therefore memory loss. When the disease sets in, its evolution is slow and the first are almost imperceptible, easily assimilated to what could happen to us when we are tired or stressed.

Alzheimer’s disease

Alzheimer’s disease is a form of progressive dementia that affects memory, behavior and thought. During the course of the disease, these attacks are unfortunately very serious and will interfere with daily life. Indeed, at an advanced stage, individuals lose their ability to hold a conversation and respond to their environment. Although the majority of those affected are over 65, this disease has nothing to do with the normal aging process. In addition, about 5% of patients are between 40 and 50 years old.

Scientists have compiled a list of 10 common symptoms found in patients:

1. Loss of memory (recently learned information, important dates, requesting the same information several times, etc.)
2. Difficulties to solve problems (difficulties in controlling numbers, following a recipe, tracking bills, etc.)
3. Difficulties to perform daily tasks at home or at work
4. Difficulties to find your bearings in time and space
5. Problems of perception (difficulty reading, recognizing colors, distances, contrasts).
6. Problems to follow conversations. People may have difficulty finding their words and will make confusion or approximations
7. Misplacement or storage in unusual places
8. Judgment problems, underestimating a problem, negligence in money management
9. Avoidance of social contacts
10. Change of mood and personality.

Histological studies on the brains of deceased patients have shown, at the microscopic level, the presence of abnormal structures on the surface and within the neurons. The first structure is called “senile plaque” and is formed by the aggregation of beta amyloid peptide. The second marker of the disease corresponds to the aggregation of the tau protein inside the neurons. This is called fibrillar neurodegeneration. This protein triggers neuronal death and would be able to migrate into the brain and therefore aggravate the disease.

Some genes and environmental factors are involved in the onset and the evolution of the disease. These discoveries prompted scientists to study various hypotheses about possible causes of the disease. For example, the intestinal flora, whose composition is driven by our lifestyle and diet, would also be involved. In fact, it seems that people with the disease have a very different flora than non-affected people. In addition, mice harboring genes that trigger Alzheimer’s disease have been treated with antibiotics and scientists have seen that the signs of the disease are less important (decrease of senile plaques). Alongside this research, scientists are also studying the role of certain viruses or sleep problems on the onset of the disease.

Some drugs have been approved in recent years. Unfortunately, none of them are effective in stopping or limiting the progression of the disease. However, many studies are in progress and aim to target the actors of the disease such as amyloid or tau protein.

Risk factors have been identified for this disease: cardiovascular problems (diabetes, hypertension or hypercholesterolemia), sedentary lifestyle, lack of intellectual activity, poor eating habits, lack of sleep or weak social interactions.

Conclusion: What can disturb our memory?

Here are 5 examples:

– Retirement
Memory, like all our cognitive abilities, needs to be solicited. And the more we use it, the less the effects of aging on our brain will be felt. Unfortunately, retirement sometimes leads to a decline in activity. According to a study by Stéphane Adam, a professor of psychology of aging, it is in the European countries where retirement is the latest, that the cognitive abilities of people over 50 decrease the least.

– Pollution
Different atmospheric pollutants (fine particles, nitrogen dioxide, etc.) have a significant neurotoxic effect and this will affect all cognitive functions, especially in sensitive subjects such as the elderly. For example, a study of people living near a dense road network (highways, outlying areas, etc.) showed that these particular living conditions affected learning, memory and language.
In children, the nervous system is not yet fully developed and is therefore vulnerable. Numerous studies have shown the existence of a correlation between air pollution, particularly due to dense road traffic, and a lower IQ, weaker visual, motor or memory faculties, retarded psychomotor development and decreased attention.

– Endocrine disruptors
Endocrine disruptors are natural or artificial foreign substances that can interfere with our hormonal system. Thus, these molecules can disturb all the major functions of living organisms: growth, reproduction, behavior, nutrition, metabolism, nervous system, and especially its development.
Endocrine disruptors are increasingly present in our daily lives. Among them, PCBs (Polycholorobiphenyl) are very dangerous and have been used to make electrical insulators, some paints or glue. PCBs are extremely polluting and their persistence in the environment and organism is high. Numerous studies have found a significant drop in the intelligence quotient of children of people contaminated by PCBs. I am thinking, for example, of those 2000 Taiwanese who had consumed PCB-contaminated rice oil in 1979. Their children were monitored and had cognitive delays. Finally, bisphenol A, a component of plastic, provided by our diet, will be dangerous during the fetal or post-natal life and can cause, in children, hyperactivity and lowering of attention, which does not promote memorization.

– Smartphones
Studies of people with addictions to smartphones have concluded that the further away the phone was from the owner, the better their cognitive abilities were. Experts therefore recommend reducing exposure, especially for young people, to limit the negative effects on well-being (fatigue, sleep disorders, stress, anxiety).

– Food and lifestyle
Sports practice promotes the appearance of new neurons, especially in the hippocampus. In the United States, on average, the daily diet consists of 12% saturated fat and 15% sugar, which is much more than recommended. However, it has been shown, both in humans and rodents that have ingested such diets, that different components of memory are disrupted and that individuals have a deficit of attention.

Bibliography:

http://www.who.int/fr/news-room/fact-sheets/detail/dementia

https://www.alz.org/alzheimers-dementia/what-is-dementia/types-of-dementia

http://acces.ens-lyon.fr/acces/thematiques/neurosciences/actualisation-des-connaissances/neuros_apprentissage/memoireapprentissage/LAROCHE-Pour_la_Science.pdf

https://www.inserm.fr/information-en-sante/dossiers-information/memoire

http://www.crfna.be/Portals/0/MdTbrochurefinale.pdf

http://www.recall-you.com/comprendre-fonctionnement-memoire/memoire-long-terme.php

https://www.sebastien-martinez.com/cerveau-et-memoire/

https://www.alz.org/fr/10-signes-et-symptomes-d-alzheimer.asp

https://www.cell.com/cell/fulltext/S0092-8674(19)31007-4?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867419310074%3Fshowall%3Dtrue

https://alzheimer-recherche.org/la-maladie-alzheimer/quest-maladie-dalzheimer/prevention/

https://lejournal.cnrs.fr/articles/la-retraite-nuit-elle-a-la-memoire